Pathogen stress is an important form of environmental extremeness and uncertainty for humans as well as other organisms. It is predicted to: fl] increase the degree of polygyny (as fewer males become appropriate mates); [2] make non-sororal polygyny more frequent (as variable offspring become more advantageous), and [3] be correlated with signs of sexual selection: physical dimorphism, societal rules about allowed wives for men in different categories, both achieved and inherited. The first two hypotheses are supported. As pathogen stress increases, the degree of polygyny increases, no matter how polygyny is measured. As pathogen stress increases, non-sororal polygyny and capture of women from outside societies increase; sororal and other endogamous forms of polygyny decrease. The third hypothesis is not supported. Measures of male-male competition and reflections of male status are not associated with pathogen stress. A man's actual present appearance (physical, behavioral) may provide a more direct and accurate reflection of a man's worth as a mate. It is possible that the measures available for testing here are not fully appropriate. These results suggest that major pathogens may have been, during human evolutionary history, an important selective force, shifting the polygyny threshold, and resulting in greater polygyny, and polygyny of specific types, in areas of high stress. The relationship appears to be of a threshold sort (at high levels of pathogen stress monogamy, polyandry, and mild polygyny are absent) rather than a linear relationship. We need within-society data for appropriate pathogens regarding relationship between individual pathogen load and probability of getting a mate, possible interactions between pathogen stress and resource accumulation in sexual selection, and impact of pathogen load on fertility.